Michael ShortPrincetonUniversity
Where’s Waldo?February 26, 2004
Hike Lab
PURPOSE: The purpose of the lab was to save a track on the GPS handheld system for a hike of several miles, to upload that data on to a computer, superimpose it over a map using GPS tracking software, and export the data to a spreadsheet to make calculations. In deciding where we should do our hike, we considered the fact that I needed some groceries, so we chose McCaffrey’s at the PrincetonShopping Center as our destination, with the acquisition of food a secondary objective to the hike.
EXPERIENCE OF THE HIKE: We started at Dillon Gym on Sunday at around 11 am. I had figured out how to get to the grocery store, so we set off in that direction. Eventually, though, we felt like we had gone too far on Nassau street, and luckily my partner Jonathan had brought a map. Turned out I’m an idiot and couldn’t read the map online properly, so we had indeed gone too far. We turned around and decided to walk on the other side of the street to see if the GPS was accurate enough to tell that. Based on the uploaded track, it was. We got to the grocery store, and I went for about half an hour while Jonathan waited outside, so that the GPS devices would keep getting reception. I marked the store as a waypoint, so that I’ll always be able to find the place. We left the store, and headed back along a different route, through the neighborhoods and past the little school with the football field. We also walked past the music school. Then, in the dramatic climax of the trip, we spotted a raccoon running up somebody’s driveway, so we observed it, and I marked it as yet another waypoint. Eventually we staggered back onto campus.
OVERALL TRIP STATS:
Total distance: 3.45 miles
Moving time: 1 hour 8 minutes
Stopped time: 30 minutes, 49 seconds
Max speed: 11.5 mph (I doubt it…)
Moving avg: 3.0 mph
Overall avg: 2.1 mph
OBSERVATIONS OF THE MAP AND THE SPREADSHEETS/GRAPHS: It was really awesome to overlay our route on a photographic map of the area. Pretty cool how well it matched up. I did notice, however, that the signal seemed to come in and out a few times, as can be seen by the gaps along our route on the map. I’ve determined this to be because occasionally my hands got cold, so I held the receiver in my pocket. I did bring it out a few times to see if it was still working, and I thought it was, but I guess I was wrong. This error could also be responsible for why the thing thought our max speed was 11.5 mph. Maybe it didn’t realize what was going on when it got the signal back. Another interesting thing is the apparent gradual gain in our speed during the time period when we were at the grocery store. Its pretty visible in the middle section of the speed versus time graph. On the distance v time graph though, its obvious that our position was constant throughout that time—we weren’t moving. Our hypothesis here is that when Jonathan had the receiver outside the store, it wasn’t moving anywhere, so it refused to save the data from the satellites and plot them as points along the route, since we weren’t moving. Therefore, the memory would only have record of the last entries before we stopped, and the first ones before we moved again. It could only conclude that there was a gradual increase in speed throughout that interval of stoppedness. The odometer is obviously working off of a different set of data than the speedometer though, since there was no similar error with regards to distance traveled.
REMARKS REGARDING THE SPREADSHEET/CALCULATIONS:
Once I exported the data from Expert GPS to the excel spreadsheet, and figured out how to export the important data, I set to work making calculations. Used distance formulas with the latitude and longitude and radius of the earth to calculate the distance traveled for each leg of the recorded trek. Of course that info was in meters, so I “cranked up the factor-label machine” to convert the leg distances according to the GPS software from miles to meters, to make sure my calculations were close enough to be within a reasonable margin of error. On the included spreadsheet, the bold columns represent my calculations. Did the same sort of thing for speed, using basic rate formula, and again the factor label machine for comparison.
CONCLUSIONS:
It worked pretty well. I just have to keep the receiver out of my pocket.
And today is an average fishing day.